Field of the Invention
The present invention relates to a metal gasket which is used as a seal means of a joint portion between an exhaust manifold and an exhaust pipe of an internal combustion engine and a joint portion between a cylinder block and a cylinder head, and a manufacturing method of the metal gasket.
Description of the Conventional Art
A metal gasket which is used as a seal means of a joint portion between an exhaust manifold and an exhaust pipe of an internal combustion engine or between an intake manifold and an intake pipe is pinched between joint surfaces which faces to each other, and is structured such as to seal exhaust gas and air-fuel mixture of air and fuel by a seal bead which is bending formed so as to surround an opening portion which is open to the joint surface.
Here, in the case of the exhaust manifold and the intake manifold, an opening shape in the joint portion in relation to the exhaust pipe or the intake pipe is non-circular shapes (for example, a rectangular ring shape), and a metal gasket having a seal bead formed into a similar shape to the opening shape is used in this portion (refer, for example, to Japanese Unexamined Patent Publication No. 08-014394). However, the metal gasket tends to deform in a portion in which the seal bead extends linearly rather than a portion extending like a curve, when the metal gasket is exposed to a fastening load. Accordingly, there is a problem that leakage tends to be generated in the linear portion of the seal bead due to lack of surface pressure. In order to solve the problem mentioned above, it has been known to secure the necessary surface pressure by enlarging a width and a height of the seal bead in the portion in which the surface pressure short tends to be generated, thereby enhancing a rigidity (refer, for example, to Japanese Unexamined Patent Publication No. 08-159284).